<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8" />
		<meta name="viewport" content="width=device-width, initial-scale=1">
		<title></title>
		<style type="text/css">
			.box {
				position: relative;
				width: 100%;
				height: 200px;
				background: #f00;
			}
			.box:after{
				position: absolute;
				left: 0;
				right: 0;
				bottom: -100px;
				content: '';
				z-index: 1;
				height: 200px;
				width: 100%;
				border-radius: 50%
				background: #fff;
			}
		</style>
	</head>
	<body>
		<div class="box">
			
		</div>
	</body>
</html>